1. Field of the Invention
The invention relates to the art of axle/suspension systems for wheeled vehicles. More particularly, the invention is directed to the art of leading and trailing arm axle/suspension systems of heavy-duty vehicles, such as tractor-trailers or semi-trailers, which cushion the vehicle ride for occupants and cargo and stabilize the vehicle during operation.
2. Background Art
Heavy-duty vehicles, such as tractor-trailers or semi-trailers and dump trucks, typically include one or more suspension systems that connect the frame of the vehicle to the wheel-bearing axles of the vehicle. These suspension systems serve several purposes. Specifically, as a vehicle is traveling over-the-road, the wheels encounter various conditions which cause various forces, loads and/or stresses to be imposed on the axle and in turn the suspension assemblies which support the axle. These include impacts caused by vertical movement as well as roll or sway, which are associated at least in part with the suspension system. More particularly, while it is desirable for a suspension system to provide a cushioned, soft ride through means such as an air suspension, the system also must be designed to control the amount of sway imposed on the vehicle, and also stabilize the vehicle, such as by including a fairly rigid suspension structure. However, in order to prevent failure of the components of the system because of an overly rigid structure and to provide some tolerance for single-wheel impacts and the like, this rigidity must be offset or tempered by some degree of roll compliance in the suspension system.
Prior art leading or trailing arm axle/suspension systems include air suspension systems, which typically include air springs for cushioning and shock absorbers for dampening. More particularly, the air springs and shock absorbers cushion the impact on the vehicle frame that is caused by vertical movement as the vehicle travels over-the-road and encounters changes in road height, such as pot holes, bumps, etc. The axle of the leading or trailing arm axle/suspension system acts as a very large anti-sway bar to help control rolling movements of the vehicle as it travels over-the-road, and rubber pivot bushings are utilized to connect the suspension beams to the vehicle frame and are softer in the vertical direction than in the fore-aft horizontal direction. Such TRI-FUNCTIONAL® bushings, as they are known in the art and which is a registered trademark of The Boler Company, the assignee of the present invention, exhibit compliance so that a certain degree of roll can be maintained, while the other components of the suspension assemblies remain relatively rigid and non-compliant.
Another type of leading or trailing arm axle/suspension system is commonly referred to in the art as a “two pin axle connection” air suspension system. These axle/suspension systems include rigid trailing arm beam weldments that bolt onto axle seats via a pair of pins, which in turn are welded to the axle. To achieve roll compliance in the structure, the two pin axle connection systems utilize rubber bushings in the axle seats, as well as in the pivot joints that connect the trailing arms to the vehicle frame.
Still another leading or trailing arm axle/suspension system is a spring beam-type air axle/suspension system, which includes trailing arms that are very stiff and thick leaf springs that are rigidly attached to the axle and are pivotally mounted to the vehicle frame. The leaf springs provide the roll compliance for the system.
However, while all of the above-described axle/suspension systems of the prior art achieve their desired result of cushioning the vehicle ride and stabilizing the vehicle, they each involve multiple specialized components that increase manufacturing costs and contribute to increased weight of the vehicle, which in turn adversely affects the fuel efficiency of the vehicle. Moreover, the components typically used in such prior art systems include components which require frequent repair or replacement.
The above-described problems of prior art axle/suspension systems are solved by the present invention through the use of an integrally formed composite structure which replaces traditional suspension beams and axles with a composite plate structure that exhibits roll compliance throughout the entire structure, rather than through just one or two discrete components such as the TRI-FUNCTIONAL® bushings, the axle seat bushings of the two-pin suspension system, and the monoleaf springs of the spring beam-type suspension systems.